The present invention relates to a blade attachment/detachment mechanism for a cutting bit, such as a saber saw, that is reciprocally driven by a drive motor.
Electric powered saber saws are used for cutting workpieces, such as pipes, wood, and steel materials, for building, repairing, and dismantling houses and other buildings. As is well known in the art, the saber saw has a reciprocally moving shaft, referred to as plunger hereinafter, that is driven to move reciprocally in a linear or circulation path within the casing of the saber saw. A linear saw blade is attached to the plunger and driven to move reciprocally at a position outside the casing of the saber saw in order to cut a workpiece.
Normally, the plunger moves reciprocally with a stroke of from about 20 mm at a minimum to about 32 mm at a maximum. For this reason, when actually cutting a workpiece, only a region of the blade that reciprocates with the stroke locally contacts the workpiece so that region of the blade wears down rapidly. As a result, the blade must be frequently replaced, particularly when the saber saw is used to cut through hard materials, such as steel. Also, the blade is long and thin and driven reciprocally at a high speed. Therefore, repulsion force generated during normal cutting operations may be imparted on the local blade portion to which the plunger is attached. In this case also, the blade needs to be replaced.
The blade is formed with an engagement hole and the saber saw includes a blade holder for enabling attachment and detachment of the blade. The engagement hole is formed in the end of the blade that is attached to the plunger. The blade holder includes a protrusion that can be inserted into the hole of the blade. By tightening or loosening the blade holder using a wrench, for example, the blade can be attached to or detached from the plunger. However, this mechanism is troublesome to use, which lowers efficiency of saber saw operations. Also, the operator must always have a wrench or other tool for attaching and detaching blades. Further, if the user looses the tool, he or she will be unable to attach and detach blades.
U.S. Pat. Nos. 5,443,276, 5,575,071, and 5,647,133 disclose toolless blade attaching and detaching mechanisms that enable exchanging blades without using a wrench or similar tool. The disclosed toolless blade attaching and detaching mechanism have a steel ball or a movable locking pin which is engagable with a hole in the blade. The movable locking pin has a front end projection formed into a conical shape. A lever or a rotary ring is provided in a main body of a saber saw to urge the movable locking pin or the ball toward the blade to hold the blade, and to provide a space capable of permitting the steel ball or the movable locking pin to be disengaged from the blade.
However, these conventional toolless blade attaching and detaching mechanism basically force the operator to touch the blade by the operator's finger in order to remove the blade from the engagement hole. When the blade is broken at it proximal end, a small piece of the blade will be left in a narrow space of the plunger. In such a case, it would be impossible to directly handle the blade with the finger. Therefore, it is a time-consuming operation to completely remove such a small piece remaining in the narrow space of the plunger.
The blade attaching and detaching mechanisms disclosed in the U.S. Pat. Nos. 5,443,276 and 5,647,133 include complicated parts that are exposed outside the saber saw. The exposed parts can be damaged by being pinched by or colliding with the workpiece during a sawing operation. Because the blade attaching and detaching mechanisms itself can be damaged in this way, it lacks proper durability.